The invention relates to an arrangement comprising an evacuated space or a space filled with an inert gas and a semiconductor device for producing an electron beam with a first cathode comprising a semiconductor body having at a major surface at least one region which emits electrons in the operating condition.
The invention further relates to semiconductor devices for use in such an arrangement.
An arrangement of the kind mentioned above is known from Netherlands patent application No. 7905470 laid open to public inspection on Jan. 15, 1981. This Application discloses a cold cathode, whose operation is based on avalanche multiplication of electrons when a pn junction is reverse-biased. The pn junction, at the area of the emitting surface, has a reduced breakdown voltage and is separated in situ from the surface by an n-type conducting layer having such a thickness and doping concentration that at the breakdown voltage the depletion zone does not extend as far as the surface, but remains separated therefrom by a surface layer which is sufficiently thin to transmit the generated electrons.
In order to reduce the work function for the electrons generated in the semiconductor body, the emitting surface is generally coated with a material reducing the work function, such as, for example, caesium or barium.
Such cathodes are generally used in vacuum tubes for recording or reproducing purposes, but may also be used in apparatus for Auger spectroscopy, electron microscopy and electron lithography. In addition to reverse-biased junction cathodes, varius other kinds of semiconductor cathodes are possible, such as, for example, NEA cathodes and field emitters.
These cathodes or semiconductor devices, in which these cathodes are integrated, are arranged after their manufacture in, for example, cathode-ray tubes or other kinds of vacuum spaces. Although this operation is carried out with great care, a light oxidation may nevertheless occur, for example, during transport. Furthermore, after such a cathode has been mounted, the concentration of oxygen atoms at the emitting surface of this cathode may increase further due to interactions of the surface layer with residual gases from the vacuum system. The presence of oxygen atoms in bound form or adsorbed at the emitting surface leads to a considerable decrease of the emission efficiency.